1. Field of Invention
This invention relates to a low-cost, improved side bearing for railcars. Specifically, it relates to the bearings that are mounted between the railcar body and the trucks of railcars. Such bearings are needed to reduce the rocking forces of the railcar about the center plate of the railcar truck, to provide support for the railcar on the truck, and to reduce the yaw rotation of the railcar that results from the "hunting" of the wheels for the track. This hunting is reduced and opposed by the frictional forces between the railcar body and the side bearing of this invention.
2. Related Art
Side bearings, per se, are not new. Indeed, they have been long used on railcars and they are the subject of several prior patents. Illustrative of these prior patents is U.S. Pat. No. 4,712,487 which issued to Miner Enterprises, Inc. on a prior application by the present inventor. Like the present invention, that patent discloses a side bearing bottom housing and a top cap with a spring positioned between the two to urge the cap upward and into constant contact support of the railcar. In addition, this prior patent also discloses a spring of the same material as the present invention--a spring formed of a copolyester polymer elastomer. Another prior patent is U.S. Pat. No. 4,793,720 which issued to American Standard Inc. on an application of Walter H. Merker. Like the applicant's earlier patent, this American Standard patent also has a bottom housing, a top cap and a copolyester polymer elastomer spring.
The elastomer spring concept of both of these earlier patents is formed of a copolyester polymer elastomer such as that sold under the trademark Hytrel.RTM. by E. I. DuPont de Nemoirs & Co. The spring and the general method of making the spring from this elastomer was invented by David G. Anderson, another employee of Miner Enterprises, Inc. Several embodiments of Anderson's spring and the method of making it are disclosed in Anderson Pat. No. 4,198,037. Other embodiments of this spring are disclosed in a later Anderson U.P. Pat. No. 4,566,678 which also issued to Miner Enterprises, Inc. This patent is similarly directed to an elastomeric pad formed of a thermoplastic Hytrel.RTM. that was joined to metal plates and intended to be used in a railcar buffer unit as well as other shock absorbing applications. The subject matter of these two Anderson patents is incorporated by reference into this application.